There are a number of treatments that require a transperineal guidance systems. For example, brachytherapy is performed with the patient in the lithotomy position, using an ultrasound imaging probe placed in the rectum to monitor seed placement. A template grid arrangement, which is kept in precise linear orientation with the ultrasound probe, must be accurately oriented adjacent the perineum in relation to the prostate, and locked in position throughout the procedure to achieve optimum seed placement. Precise and reproducible orientation and positioning of the ultrasound imaging probe in the rectum is a key element in both the calculations required for determining the number and distribution of radioactive seeds required for treatment and their subsequent placement using preloaded needles guided by the perineal template and real time ultrasound imaging. Even with proper probe positioning, placement of the seed-delivering needles using the template grid needs to be accurate and precisely coordinated with the images from the probe and the patient's anatomy to have effective therapy.
One commonly available template grid used to guide placement of the needles is a relatively thick block (approximately 2 cm in thickness) of plastic or metal with multiple machined parallel holes arranged in a matrix and spaced at 5 mm intervals. An example of such a template grid is the needle guidance template used with the ULTRA-STEP™ stepping device available from Civco Medical Instruments of Kalona, Iowa. The template grid needs to be thick to have accurate needle placement by ensuring the needle is inserted perpendicular to the face of the template grid. As these block template grids are reused on different patients, one area of potential risk is microbial cross-contamination. Although the template grids are chemically and physically washed and then sterilized between uses, the geometry and small size of the needle holes in the matrix makes reliable sterilization extremely difficult. As the cleaning and sterilization procedures can be quite time consuming, a reusable template grid has a significant amount of “down time” during which it cannot be used.
Disposable template grids, which essentially eliminate the possibility of cross-contamination and the other problems associated with reusable grids, are commercially available. One design uses a series of thin plates held in parallel and aligned by welded or machined brackets. One example of such a design is the template available with the brachytherapy ultrasound system sold by Carolina Medical Inc. of King, N.C. Spacing the plates apart from each other ensures that the needles are inserted perpendicular to the face of the template grid. The multi-plate design does make cleaning and sterilization less problematic and also eliminates some of the manufacturing difficulties of the thick block design. The down time due to cleaning and sterilization, however, remains essentially unaffected. Furthermore, the manufacturing costs involved in accurately and securely aligning, spacing, and joining the plates make producing a disposable multi-plate template grid unrealistic. Another design, disclosed in U.S. Pat. No. 6,036,632, is an injection-molded completely disposable template grid. A template grid that used less disposable material or disposable material that is available at a lower cost than injection-molded material would be advantageous.
Thus, there exists a need for an improved template grid.